1. Field
The presently disclosed subject matter relates to a lighting lamp such as a lamp for a vehicle, and more particularly relates to a configuration of a lighting lamp employing at least one LED lamp used as a light source thereof.
2. Description of the Related Art
A conventional lighting lamp using a filament bulb as a light source uses a filament, and, when turned on, the temperature of the filament gradually increases as time elapses, and the lamp arrives at a predetermined brightness and becomes stable upon reaching a state where a prescribed current flows. This powering up state can be observed from the outside and presents a rise of brightness, which is extremely short, but is sensible.
Moreover, upon turning off the lighting lamp, the current to the filament, which is providing light via incandescence due to electricity that is present, is shut off, and thus the temperature of the filament gradually decreases, and the brightness also gradually falls. A comparison of the change in the illuminance upon turning on with that upon turning off reveals that since forced heating is carried out by the impressed current upon turning on, the rise seems faster, and, on the other hand, since the filament is spontaneously cooled upon turning off, the fall seems slower than the rise.
Recently, semiconductor light emitting elements such as LED lamps 93 shown in FIG. 6 have increasingly been employed as a light source for a lighting lamp 90 because, among other reasons, they do not require a disconnection of a filament, and have a semipermanent life, resulting in simpler maintenance. The LED lamp 93 turns on while emitting a prescribed quantity of light immediately after the impression of a power supply, and turns off completely immediately after the shut off of the power supply, which is different from the above-described filament bulb.
As a result, the LED lamp suddenly turns on and off as compared with a lamp that uses a filament bulb for a light source, which can give an unpleasant sensation to a driver of a following vehicle, and may not give a sense of high quality. Thus, there has been proposed a circuit provided with a control unit 91 and a drive device 92 including a drive unit 92a such as the electronic relay as shown in FIG. 6. Upon turning off the circuit, which especially tends to give an unpleasant sensation to observers, a duty ratio of the voltage impressed on the LED lamps 93 is gradually lowered to reproduce a turn-off state that is close to that of a filament bulb as shown in FIG. 7 (refer to Japanese Unexamined Patent Publication (Kokai) No. 2003-347594).
However, since the LED lamp does not provide light almost immediately upon turning off the power supply as described above, if the off-duty portion of the cycle becomes wider as compared with the on-duty portion of the cycle, flickering may be sensed more dominantly instead of the intended decrease of brightness. Thus, it may be necessary to rapidly turn off the LED lamp after the brightness decreases to a certain degree, which is far from an accurate or complete reproduction of the spontaneous turn-off characteristics of the filament bulb.
Furthermore, if a light emitting body which is configured to provide the complete flickering as described above is viewed in a lateral direction while the light emitting body is traveling at a relatively high speed, the light emitting states and extinct states may appear as a dotted line. Thus, the drive device 92 as described above may further increase the unpleasant sensation to an observer.